They'll have the ship off-loaded by 10 am. 10:30 latest. It's about 15 minutes to the airport, pending the availability of taxis. Your time to check in will vary, because of the volume of other cruisers also trying to check in at the same time. Remember, your's is not the only ship cycling (arriving/departing) that day. With an average of 2,300 passengers per ship; you could very well be looking at an extra 27,600 passengers trying to get into and out of the Miami airport that morning!
My recommendation? If at all possible, schedule yor flights for the day before and the day after your cruise. 1) if you are late arriving, the airline will have time to find and get your luggage to you before the ship sails, 2) you'll be among the last to depart the ship because they cruise line will try (no guarantees here) to get passengers leaving that day, off first, and 3) you'll avoid the intense crowds at the airport.
